1. Field of the Invention
The present invention concerns a gas combustion method for catalytic flameless combustion of a gas mixture comprising air and a liquefied gas such as a butane gas by using a combustion catalyst, as well as an apparatus used therefor and, more in particular, it relates to an improvement to the system for transferring a combustion mode from flaming combustion upon ignition to aimed catalytic flameless combustion.
2. Description of the Prior Art
Gas combustion apparatus using a liquefied gas as a fuel gas is generally classified into a well-known torch lamp type apparatus that directly utilizes heat obtained by flaming combustion and a so-called catalytic combustion apparatus for flameless combustion of an air/fuel gas mixture by using a combustion catalyst as described, for example, by A. Fujiwara in U.S. Pat. No. 4,133,301.
By the way, when a massive and solid catalyst is used as a combustion catalyst in the catalytic gas combustion apparatus, it is necessary that the combustion catalyst is at first heated to an oxidizing reaction temperature by a pilot flame of flaming combustion and that the pilot flame is extinguished subsequently and the gas mixture is directly supplied to the heated combustion catalyst.
For extinguishing the pilot flame, U.S. Pat. No. 4,552,124 discloses a structure in which an opening disposed to a combustion chamber is closed by a shutter mechanism and U.S. Pat. No. 4,688,551 proposes a structure in which an air intake port of a gas mixture generation member is once closed wholly by a air flow rate control member after igniting a pilot flame.
In the existent pilot flame extinguishing means described above, the former method of using the shutter mechanism requires a movable shutter member to the combustion chamber. In addition, since the opening is kept open during flaming combustion, it may possibly lead to flashing danger in a case where flammable material is present near at hand.
On the contrary, since the latter method uses the operation member for extinguishing the flame by the change of the air/fuel gas mixing ratio, it can save the opening and the shutter to be disposed to the combustion chamber if the size of the combustion chamber is large enough. Accordingly, there is no risk of catching fire even if flammable material is present near at hand. However, when the air intake port of the operation member is wholly closed upon extinction of the pilot flame, since a fuel gas not containing air at all is not burnt by the combustion catalyst but discharged as it is to the outside. This may cause a danger that the fuel gas flames up at the outside of the apparatus through it is only momentary.